Motion capture for performance art

ABSTRACT

A method for controlling aspects of an artistic performance with a motion capture system includes modeling movements of a performer with a biomechanical skeleton, selecting parent and child segments on the biomechanical skeleton, positioning motion capture sensors on a motion capture subject at positions corresponding to the parent and child segments, selecting actions associated with movements of the child segment according to positions of the parent segment within at least two predefined spatial zones, executing actions in a first action group for the child segment when the parent segment is in a first spatial zone, and executing actions in a second action group for the child segment when the parent segment is in a second spatial zone.

FIELD OF THE INVENTION

Embodiments are generally related to motion capture methods formeasuring linear and/or rotational displacements of parts of a person'sbody, and more particularly to using predefined spatial boundaries withmotion capture measurement data to select or modify aspects of anartistic performance.

BACKGROUND

Motion capture may be performed by positioning a measurement sensor suchas an inertial measurement unit (IMU) against a person's body andrecording data values from which may be determined changes in angularvalues, linear displacements, and/or rates of movement for the part ofthe body to which the IMU is attached. Motion capture may alternativelybe accomplished with cameras or other non-contact position-sensingapparatus. Data from motion capture sensors may be used to form akinematic model, a mathematical model of the positions and movements ofthe motion capture subject. A biomechanical skeleton is an example of akinematic model. The measured changes in positions and rates of movementof the measured body locations on the motion capture subject may beapplied to corresponding movements and positions of rigid segments androtatable joints in the biomechanical skeleton. A separate IMU may bepositioned on the motion capture subject at each part of the person'sbody to be represented by a segment and/or joint in the biomechanicalskeleton, or IMU data may be extrapolated to estimate the positions ofsome segments and joints in the biomechanical skeleton.

The kinematic model representing the motion capture subject may be usedto operate an apparatus through computer activation of suitableactuators. For example, a biomechanical skeleton configured to emulate aperson's movements and body positions may be used to operate a machine,a tool, a vehicle, a musical instrument, a computer keyboard, ajoystick, a lighting control panel, an audio synthesizer, or otherdevices, without the person represented by the kinematic model cominginto physical contact with the device being operated.

A kinematic model may be used to control a computer simulation of anactual or imagined apparatus. The simulated apparatus may be referred toas a “virtual device”. The virtual device may access audio files orvideo files which can be modified by interaction with the kinematicmodel representing movements of the motion capture subject. Thekinematic model and the virtual device may appear as components of acomputer-generated scene to give audible and visual feedback to a motioncapture subject and to present actions associated with the motioncapture subject's movements to others. More than one kinematic model maybe presented in a computer-generated scene, each kinematic modelpossibly corresponding to a different motion capture subject, therebyenabling collaborative or competitive activities by persons separatedfrom one another spatially or temporally. Alternately, kinematic modelsrepresenting actions by one person at different locations or differenttimes may be presented together to create a “self-collaboration”.

Dancers, musicians, and other performance artists may use motion capturegloves or other wearable motion capture devices for creative control ofaudible and visual aspects of a performance. For example, a musician maymove their fingers over a surface or through empty space to play avirtual device representing keys on a keyboard. Or, instead ofinteracting with an emulation of a physical device like a keyboard, amusician may arrange their fingers into predefined gestures to selectpreferred musical notes or sounds, modify sound volume, modifyfrequencies present in sounds, or adjust other parameters relating tothe sound. A predetermined set of spatial positions of the performer'sfingers may have an associated predetermined set of audible and/orvisual effects. Movements outside the predetermined range may produceunexpected results or may not be recognized by the virtual device.Sounds to be produced or modified during a performance may berepresented as numerical values in a stored computer file and/or may begenerated by an audio synthesizer. Sounds may be modified concurrentlywith the musician's movements or in response to a stored motion capturerecord of the movements. Pressure sensors or momentary switches may beprovided on a glove's fingertips to allow an artist to simulate drummingor other percussive effects by tapping or rubbing the fingertips againsta surface. Visual effects such as the color, location, timing, andintensity of virtual or real light sources or images may be controlledby similar means.

Operating a virtual device with a wearable motion capture device mayimpose limitations on a performance. For example, a motion capture(“mocap”) glove configured to detect the positions of a musician'sfingers relative to the palm of the hand may be used to play a virtualdevice representing a keyboard on a piano, organ, or synthesizer. It maybe difficult for the musician to calibrate the mocap glove withsufficient accuracy to resolve small differences in finger positionsneeded to detect which octave of a keyboard is being played, or whichmanual is being played for a virtual instrument with more than onemanual.

Real instruments controlled by means other than, or in addition to,positions of a musician's fingers may be difficult to emulate with avirtual instrument operated by a mocap glove. For example, a kinematicmodel may be configured to play notes on a virtual trumpet by capturinga musician's finger motions and positions for activating virtual trumpetvalves, then triggering corresponding audio output from an audio source.Mocap gloves are available with sufficient spatial resolution to detectthe seven unique finger positions for operating the three valves on atrumpet. However, emulating a musician's finger positions for activatingvalves is not sufficient to produce the full range of notes that can beproduced by a real trumpet. By controlling tension in the lip muscles, askilled performer playing a real trumpet can produce many more than thenumber of natural tones resulting from operation of the valves.Arranging a wearable motion capture device to emulate changes in amusician's finger positions and changes in the musician's lip tension isdifficult, possibly requiring hand motions or hand positions that feelunnatural to the musician or are difficult to repeat accurately, andpossibly resulting in undesirable limitations in musical expression.

SUMMARY

An example method embodiment includes selecting a parent segment on abiomechanical skeleton; selecting a child segment connected to theparent segment; positioning a first motion capture sensor at a firstlocation on a motion capture subject, the first location correspondingto the parent segment; and positioning a second motion capture sensor ata second location on the motion capture subject, the second locationcorresponding to the child segment. The example method further includessetting a first rotational limit for a first spatial zone and a secondrotational limit for the first spatial zone for the parent segment;setting a first rotational limit for a second spatial zone and a secondrotational limit for the second spatial zone for the parent segment;setting a first action to be performed by the child segment; setting asecond action to be performed by the child segment; executing the firstaction when the parent segment is positioned in the first spatial zone;and executing the second action when the parent segment is in the secondspatial zone.

Motion by the child segment may optionally be greater than a firstmotion threshold for the first action to be performed. Motion by thechild segment may optionally be greater than a second motion thresholdfor the second action to be performed. The first motion threshold and/orthe second motion threshold may optionally be set to any one or more ofthe following conditions for a motion threshold, individually or in anycombination: setting the motion threshold to a minimum magnitude ofangular rotation; setting the motion threshold to a minimum magnitude oflinear displacement; setting the motion threshold to a minimum pressurevalue from a pressure sensor, and setting the motion threshold to aminimum magnitude of a change in a velocity of motion of the childsegment.

The example method embodiment optionally further includes defining afirst action group including a set of actions to be performed followingmotion by the child segment, wherein the first action is one of the setof actions in the first action group. A selected one of the first actiongroup is optionally performed when the parent segment is positioned inthe first spatial zone. The example method embodiment optionally furtherincludes defining a second action group including another set of actionsto be performed following motion by the child segment, wherein thesecond action is one of the set of actions in the second action group.An action group optionally represents a set of movements and/orpositions of a child segment that may be repeated at different locationsof a parent segment. Alternatively, the set of actions in an actiongroup may be different from the set of actions in another action group.

Execution of the second action may optionally be prevented when theparent segment is in the first spatial zone. Execution of the firstaction may optionally be prevented when the parent segment is in thesecond spatial zone.

The example method embodiment optionally further includes setting afirst rotational limit and a second rotational limit for each of anadditional plurality of spatial zones. Adjacent spatial zones mayoptionally have shared limits. For example, the first rotational limitfor the second spatial zone and the second rotational limit for thefirst spatial zone may optionally be set at a same value of a rotationangle of the parent segment. Alternately, the first rotational limit andthe second rotational limit for each spatial zone may be set such thatthere is an intervening space between the spatial zones.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram with examples of steps performed in thedisclosed method embodiment.

FIG. 2 is a simplified pictorial view of examples of a motion captureglove and other motion capture sensors on a person's arms. FIG. 2further illustrates examples of reference directions used herein.

FIG. 3 is a side view of an example motion capture glove in accord withthe disclosed method embodiments.

FIG. 4 is a schematic representation of a biomechanical skeleton for aright arm. The example biomechanical skeleton is positioned in the YZplane for comparison to the position of the right arm in FIG. 2 , with aviewing direction parallel to the X axis toward the back of the righthand.

FIG. 5 is a block diagram of an example motion capture system in accordwith the disclosed method embodiments.

FIG. 6 shows several example positions of the hand, forearm, and upperarm of the biomechanical skeleton example of FIG. 4 , furtherillustrating examples of rotational limits for defining spatial zonesaccording to positions of a selected parent segment.

FIG. 7 is a block diagram showing examples of steps for setting motionthresholds for a child segment.

DESCRIPTION

The disclosed example method embodiments represent movements by a motioncapture subject with a kinematic model such as a biomechanical skeleton,associate at least two alternative actions with a child segment in thekinematic model, associate a first of the alternative actions for thechild segment with a first spatial zone for a parent segment connectedto the child segment, associate a second of the alternative actions witha second spatial zone for the parent segment, and select from among thealternative actions for the child segment according to the spatial zonethe parent segment is positioned in. Each spatial zone for the parentsegment is bounded by a first rotational limit and a second rotationallimit about a selected spatial axis.

Whenever the parent segment is between the first rotational limit andthe second rotational limit for a spatial zone, the child segment mayperform the action or actions associated with the spatial zone in whichthe parent segment is located. When the parent segment moves to adifferent spatial zone, a different set of actions may be performed bythe child segment, even when the parts of the child segment are in asame spatial relationship to one another in both spatial zones, or partof the child segment is on one spatial zone and another part of thechild segment is in another spatial zone.

As an example, consider a performance artist playing a virtualrepresentation of an electronic organ. The artist may wear a motioncapture (mocap) glove or similar equipment to detect and record theangles between the fingers on a hand. Sufficient movement of the fingersmay trigger audio output associated with keys on a virtual keyboard,i.e., the artist is controlling the production of sounds by “playing” akeyboard that is not physically present. A particular arrangement of thefingers, and of the corresponding segments and joints in a biomechanicalskeleton representation of the artist's hand, may be used by the artistto create the same combination of virtual keys in more than one octaveof the virtual keyboard. It may be difficult, however, for the artist toconfigure a mocap glove alone to recognize when a hand is positioned inone octave or another octave for the same arrangement of the fingers.Similarly, it may be difficult to configure the mocap glove to recognizewhich manual of a multi-keyboard instrument a same configuration of thefingers is intended to play.

Using a mocap glove alone may lead to uncertainty about which part of avirtual instrument a particular arrangement of the fingers is beingapplied to. The disclosed method embodiments resolve this uncertainty bychanging the actions assigned to each finger according to a detectedangle of the parent segment. The parent segment may be, for example,either the forearm or upper arm according to the performer's preference.When the measured rotational angle of the parent segment falls in aselected spatial zone, the child segment activates virtual keys, levers,valves, switches, etc. assigned as an action or action group to thatspatial zone for the virtual instrument. When the parent segment ispositioned in another spatial zone, the child segment produces adifferent set of effects assigned to a second action group, the secondaction group possibly corresponding to a different location on thevirtual instrument, or alternatively effects from a different virtualinstrument.

In some embodiments, spatial zones are nonoverlapping and may optionallybe separated by intervening space from one another. Adjacent spatialzones may optionally have a shared rotational limit. Spatial zones mayalternately be partially overlapping at the discretion of the artist.Spatial zones may optionally be separated from one another with respectto some rotational axes and partially overlapping with respect to otherrotational axes.

The example embodiment is effective for performing on a virtual keyboardsimulating a full size, multi-manual keyboard instrument. In otherapplications, an example embodiment enables a performer to play avirtual instrument when the corresponding real instrument requiresmovements in addition to or instead of hand movements. For example, aspreviously noted it is difficult to emulate a trumpet and some otherbrass instruments with a motion capture glove alone because providing afunction corresponding to a change in the performer's lip tension isdifficult to implement. The example method embodiment can resolve thisproblem by assigning to a child segment, for example a child segmentrepresenting a hand wearing a mocap glove, a group of notes in aselected octave to the complete set of discrete finger positionsassociated with operating the valves on the real trumpet, andassociating the group of notes with a spatial zone defined for a parentsegment. The parent segment may be, for example, the forearm and/orupper arm at the performer's discretion. A different set of notes, forexample notes in another octave, may be assigned to the child segmentwith the same finger positions detected by the mocap glove, i.e. thesame valve positions on the real trumpet, but for the parent segmentmoved into another spatial zone. The performer's movement of the parentsegment from one spatial zone to another causes a corresponding changein the set of notes associated with movements of the child segment,leading to a transition from one set of notes in a first action group toa second set of notes in the second action group for the child segment.A performer may find it reasonably intuitive to shift octaves by tiltingthe virtual trumpet by raising the forearm and/or upper arm, but maychoose another action of the parent and child segments if desired.

The disclosed method embodiments are further effective for performancesusing virtual devices having no physical counterpart. For example, aperformance artist may control audio effects with one virtual device andvisual effects with another virtual device with both virtual devicespositioned in a virtual performance space. Functions associated withaudio effects may be associated with movements of a child segment for aparent segment, e.g. the upper arm, positioned in one spatial zone, andfunctions associated with video effects may be associated with movementsof the child segment with positioning of the parent segment in anotherspatial zone. Associating sets of actions for a child segment withspatial zones for a parent segment allows many more actions to beperformed than could easily be represented by a motion capture glovealone.

FIG. 1 shows some steps included in an example method embodiment 100.The method embodiment 100 begins at step 1000 by modelling a motioncapture subject with a biomechanical skeleton. Next, at step 1002 aparent segment is selected on the biomechanical skeleton. A childsegment connected to the parent segment is also selected, with thepreferred relationship that moving the parent segment also moves thechild segment, but moving the child segment may not move the parentsegment.

At step 1004, a mocap sensor is positioned at a first location on themotion capture subject, and a second mocap sensor is positioned at asecond location on the motion capture subject. Examples of a mocapsensor include, but are not limited to, an IMU and a pressure sensor.One of the mocap sensors is preferably positioned at a location on themotion capture subject corresponding to the parent segment of thebiomechanical skeleton. Another mocap sensor is preferably positioned onthe motion capture subject at a location corresponding to the childsegment of the biomechanical skeleton.

At step 1006, a first rotational limit and a second rotational limit areset as boundaries for a first spatial zone. The parent segment may beconsidered to be within the first spatial zone when positioned betweenthe first and second rotational limits and optionally when positioned atone of the rotational limits. Each pair of rotational limits applies toa selected spatial axis sensed by the motion capture apparatus. Aspatial zone may have first and second rotational limits for any onespatial axis, additional rotational limits for any two mutuallyperpendicular spatial axes, or rotational limits for all three mutuallyperpendicular spatial axes.

At step 1008, first and second rotational limits are set for a secondspatial zone. As for the first spatial zone, the second spatial zone mayhave first and second rotational limits for any one spatial axis,additional rotational limits for any two mutually perpendicular spatialaxes, or rotational limits for all three mutually perpendicular spatialaxes.

At step 1010, a first action to be performed following motion by thechild segment is set. Optionally, a first action group is defined forthe child segment, with the members of the first action group possiblyincluding actions assigned to selected elements of the child segment.For example, when a child segment is a hand of a biomechanical skeleton,an action group may be specific sounds associated with each finger. Anaction of a child segment may refer to a signal for activating anactuator or a parameter for adjusting the contents of a previouslystored computer file.

At step 1012, a second action to be performed following motion by thechild segment is set. Optionally, a second action group is defined forthe child segment, with the members of the second action group possiblyincluding actions assigned to selected elements of the child segment.

As suggested at step 1014, the example method embodiment performs thefirst action defined for the child segment when the parent segment ispositioned in the first spatial zone. Alternately, the method performsany one or more of the actions from the first action group when theparent segment is positioned in the first spatial zone.

As suggested at step 1016, the example method embodiment performs thesecond action defined for the child segment when the parent segment ispositioned in the second spatial zone. Alternately, the method performsany one or more of the actions from the second action group when theparent segment is positioned in the first spatial zone.

When the first action is performed in response to presence of the parentsegment in the first spatial zone, the method optionally includespreventing performance of the second action. When the second action isperformed in response to presence of the parent segment in the secondspatial zone, the method optionally includes preventing performance ofthe first action.

FIG. 2 shows examples of positions of motion capture sensors suitablefor use with the example method embodiments. A representation of aperson facing the viewer is shown with an example of a mocap glove 114worn on the right hand 246, an example of a forearm inertial measurementunit (IMU) 116 attached to an elastic band 240 worn on the right forearm244, and an example of an upper arm IMU 118 attached to another elasticband 240 worn on the right upper arm 242. The forearm IMU 116 furtherrepresents a first mocap sensor location 248 optionally corresponding toan example of a parent segment 192 of a kinematic model. The mocap glove114 further exemplifies a second mocap sensor location 250 optionallycorresponding to a child segment 194 of a kinematic model. Other partsof the kinematic model may optionally be selected as the parent segmentor child segment. A set of right arm sensors 158 including the motioncapture glove, forearm IMU, and upper arm IMU are optionally duplicatedin a set of left arm sensors 160.

FIG. 2 further shows examples of directions 300 referenced herein. The Zaxis extends vertically from a surface upon which the person standstoward the person's head. The X axis extends transversely in ahorizontal plane parallel to the surface upon which the person stands.The Y axis extends toward the viewer from plane of the drawing.Referencing the example directions 300, rotating the right arm at theshoulder joint so that the forearm and hand point at the viewerrepresents a rotation of the shoulder joint about the X axis.

FIG. 3 shows a side view of a mocap glove 114 in accord with the examplemethod embodiment 100. Attached to the thumb of the glove are examplesof a first IMU1 120 and a second IMU2 122. Attached to the index fingerof the glove 114 are examples of a first IMU1 124, a second IMU2 126,and a third IMU3 128. A carpal IMU 162 positioned on the back of theglove captures position and/or rotation data for kinematic modelsegments and joints representing positions and/or rotations of the backof the mocap subject's hand. The example method embodiments 100 areoperable with fewer than the number of mocap sensors represented by IMUsin FIG. 3 .

FIG. 4 shows an example kinematic model of a right arm. The examplekinematic model is implemented as a biomechanical skeleton 164 withrigid segments 166 coupled to one another through intervening rotatablejoints 168. As suggested in the figure, rigid segments may be shown asmathematical line segment entities. Rigid segments may alternatively bepresented as geometric shapes having surfaces and volumes. As usedherein, a rigid segment is a mathematical model of an ideal structuralelement having no flexibility, i.e., the rigid segment does not deflectwhen placed under a load.

In the example biomechanical skeleton 164 of FIG. 4 , a rigid upper armsegment 170 extends from a rotatable shoulder joint 172 to a rotatableelbow joint 176. A rigid forearm segment 174 extends from the elbowjoint 176 to a rotatable wrist joint 178. One or more rigid segments 190representing the metacarpal bones of the motion capture subject's handextend from the wrist joint 178 to rotatable joints 168 at the base ofthe thumb 180, first finger 182, second finger 184, third finger 186,and fourth finger 188. Each finger and the thumb are further optionallymodeled with rigid segments 166 and rotatable joints 168 simulating thephalanges and joints of a human hand. As suggested in FIG. 4 , a parentsegment 192 may optionally be selected to include the shoulder joint 172and upper arm segment, and a child segment may optionally be selected toinclude the elbow joint 176, the forearm segment 174, and all thesegments and joints of the wrist and hand. Other choices of parentsegment and child segment are also possible according to the nature of avirtual device being controlled and the preferences of the personcontrolling the virtual device.

An example of a motion capture apparatus 102 in accord with the examplemethod embodiment 100 is shown in FIG. 5 . The illustrated examplemotion capture glove 114 has attached to the thumb of the glove a thumbIMU1 120, a thumb IMU2 122, and a thumb pressure sensor 148 fordetecting when the mocap glove contacts a solid object. A first fingerIMU1 124, a first finger IMU2 126, a first finger IMU3 128, and a firstfinger pressure sensor 150 are attached to the first finger of the mocapglove. A second finger IMU1 130, a second finger IMU2 132, a secondfinger IMU3 134, and a second finger pressure sensor 152 are attached tothe second finger of the mocap glove. A third finger IMU1 136, a thirdfinger IMU2 138, a third finger IMU3 140, and a third finger pressuresensor 154 are attached to the third finger of the mocap glove. A fourthfinger IMU1 142, a fourth finger IMU2 144, a fourth finger IMU3 146, anda fourth finger pressure sensor 156 are attached to the fourth finger ofthe mocap glove. A mocap glove 114 may optionally include fewer sensorsthan shown in the example of FIG. 5 . The set of right arm sensors 158optionally includes any one or more of the preceding IMUs described forthe mocap glove 114 and preferably further includes at least one of theforearm IMU 116 and the upper arm IMU 118. A set of left arm sensors 160may optionally be provided, with the set of left arm sensors includingany one or more of the sensors described for the right arm sensors 158.

All IMUs and optional pressure sensors are preferably connected forsignal communication with a microprocessor (MPU) 112. An analog todigital converter (ADC) 110 may be provided to convert signals frommotion capture sensors to digital values stored in a memory 108accessible to the MPU 112. The MPU 112 may be connected for signalcommunication with other devices through a bidirectional wirelesscommunications transceiver 106. An antenna 106 is connected for exchangeof electrical signals with the transceiver 106.

FIG. 6 illustrates several aspects of the example method embodiment 100in a view parallel to the Z axis of examples of a biomechanical skeleton164. The location of the thumb 180 on the hand 196 of the biomechanicalskeleton suggests that the view in FIG. 6 may be interpreted as downwardonto the back of the right hand, although other interpretations arepossible. An example spatial volume in which a motion capture subjectmoves is preferably divided into at least two, and optionally more thantwo spatial zones, each spatial zone associated with a range ofrotational angles for a parent segment of the biomechanical skeleton. Inthe example of FIG. 6 , a virtual performance space is divided into fourspatial zones, a first spatial zone 210, a second spatial zone 212, athird spatial zone 214, and a fourth spatial zone 216. Each spatial zonecorresponds to a range of movement for an example parent segment 192represented in the example of the figure by an upper arm segment 170extending from the shoulder joint 172 to the elbow joint 176 of thebiomechanical skeleton.

In the example of FIG. 6 , adjacent spatial zones have shared rotationallimits. Other arrangements of spatial zones are possible at thediscretion of the artist. An angular range of the first spatial zone 210in the example of FIG. 6 extends from a first rotational limit 218 to asecond rotational limit 220. An angular range of the second spatial zone212 extends from a first rotational limit 222 to a second rotationallimit 224. An angular range of the optional third spatial zone 214extends from a first rotational limit 226 to a second rotational limit228. An angular range of the optional fourth spatial zone 216 extendsfrom a first rotational limit 230 to a second rotational limit 232. Allof the example rotational limits in the example of FIG. 6 apply to asame selected axis of rotation passing through the shoulder joint 172.Additional rotational limits may optionally be determined for eachspatial zone for either one or both of the remaining two mutuallyorthogonal spatial axes. Each limit may be assigned a position in thevirtual performance space by the motion capture subject moving the bodypart corresponding to the selected parent segment to a preferredlimiting angle for each spatial zone and recording the correspondingrotational limit value for the spatial zone.

Continuing with the example of FIG. 6 , for every location of a parentsegment 192 within one spatial zone, an action, or alternately a groupof actions, is set for the child segment 194. When the upper arm segment170 is positioned in the first spatial zone 210, movements of the childsegment 194 select one or more actions from an action group 236 for zone1. The action group 236 for spatial zone 1 applies to all hand positionsover the example range of rotation 234 of the hand about the wrist jointand all rotations of the forearm segment 174 about the elbow joint. Theaction group 236 may include, for example, a key to be activated on avirtual keyboard by each finger according to positions and anglesdetected by an IMU, a valve to be operated on a virtual trumpet for eachfinger, and so on according to the controls present on a virtual device.

When the upper arm segment 170 is positioned in the second spatial zone212, movements of the child segment select one or more actions from anaction group 238 for spatial zone 2. The action group 238 for spatialzone 2 applies to all positions of the child segment 194 including thehand 196 and forearm segment 174 as long as the parent segment ispositioned within spatial zone 2, as suggested in FIG. 6 . FIG. 6further shows that the action group 238 optionally applies to allpositions of the child segment 194 when the parent segment remainswithin the boundaries of spatial zone 2, even when parts of the childsegment, for example the hand and/or part of the forearm segment, rotatethrough an angle 198 or another angle 200 about the elbow joint 176and/or wrist joint 178 that cause parts of the child segment to extendoutside the boundaries for the spatial zone of the parent segment. Thesecond action group 23 may include, for example, a key to be activatedon a virtual keyboard by each finger according to positions and anglesdetected by an IMU, a valve to be operated on a virtual trumpet for eachfinger, and so on according to the controls present on a the virtualdevice, with the actions in the second action group optionally differentthan the actions in the first action group.

It may be desirable to establish motion thresholds for detecting apreferred level of motion of a child segment needed to trigger an actionassociated with a spatial zone of a parent segment. FIG. 7 includesexamples 1018 of steps for setting motion thresholds to define minimumchild segment movement needed to trigger an action such as a keyactivation or a valve activation with the biomechanical skeleton. Atstep 1020, setting a motion threshold includes setting a minimummagnitude of angular rotation measured for a child segment by an IMU. Atstep 1022, setting a motion threshold includes setting a minimummagnitude of linear displacement measured by an IMU for the childsegment. At step 1024, setting a motion threshold includes setting aminimum value of pressure measured by a pressure sensor on a mocapglove. At step 1026, setting a motion threshold includes setting aminimum magnitude of a change in velocity of motion measured by an IMU.At step 1028, setting a motion threshold includes detecting a change inthe algebraic sign of a velocity measured by an IMU. The examples ofFIG. 7 may be applied in any order and in any combination of one or moreof the example steps.

Unless expressly stated otherwise herein, ordinary terms have theircorresponding ordinary meanings within the respective contexts of theirpresentations, and ordinary terms of art have their correspondingregular meanings. Where used, the expression “and/or” relating twoelements A and B, as in “A and/or B”, is equivalent in meaning to “Awithout B, or B without A, or A and B together”.

What is claimed is:
 1. A method, comprising: forming a kinematic modelof a motion capture subject as a biomechanical skeleton including aparent segment rotatably coupled to a child segment; positioning a firstmotion capture sensor at a first location on the motion capture subject,the first location corresponding to the parent segment; positioning asecond motion capture sensor at a second location on the motion capturesubject, the second location corresponding to the child segment; settinga first rotational limit for a first spatial zone for the parent segmentand a second rotational limit for the first spatial zone; setting afirst rotational limit for a second spatial zone for the parent segmentand a second rotational limit for the second spatial zone; setting afirst action to be performed by the child segment when a rotationalangle of the parent segment is between the first rotational limit forthe first spatial zone and the second rotational limit for the firstspatial zone; setting a second action to be performed by the childsegment when the rotational angle of the parent segment is between thefirst rotational limit for the second spatial zone and the secondrotational limit for the second spatial zone; setting a motion thresholdto a minimum magnitude of angular rotation measured by the second motioncapture sensor; determining the rotational angle of the parent segmentfrom data recorded with the first motion capture sensor; determining arotational angle of the child segment from data recorded with the secondmotion capture sensor; performing the first action with the childsegment when the rotational angle of the parent segment is between thefirst rotational limit for the first spatial zone and the secondrotational limit for in the first spatial zone and the rotational angleof the child segment is greater than the motion threshold; andperforming the second action with the child segment when the rotationalangle of the parent segment is between the first rotational limit forthe second spatial zone and the second rotational limit for the secondspatial zone and the rotational angle of the child segment is greaterthan the motion threshold.
 2. The method of claim 1, further includingin the first motion threshold a minimum magnitude of lineardisplacement.
 3. The method of claim 1, further including in the firstmotion threshold a minimum pressure value of pressure from a pressuresensor.
 4. The method of claim 1, further including in the first motionthreshold a minimum magnitude of a change in a velocity of motion of thechild segment.
 5. The method of claim 1, further comprising defining afirst action group including a set of actions to be performed by thechild segment when the rotational angle of the parent segment is betweenthe first rotational limit for the first spatial zone and the secondrotational limit for the first spatial zone and the rotational angle ofthe child segment is greater than the motion threshold, wherein thefirst action group includes the first action.
 6. The method of claim 5,wherein a selected one of the first action group is performed when therotational angle of the parent segment is between the first rotationallimit for the first spatial zone and the second rotational limit for thefirst spatial zone and the rotational angle of the child segment isgreater than the motion threshold.
 7. The method of claim 5, furthercomprising defining a second action group including another set ofactions to be performed when the rotational angle of the parent segmentis between the first rotational limit for the second spatial zone andthe second rotational limit for the second spatial zone and therotational angle of the child segment is greater than the motionthreshold, wherein the second action group includes the second action.8. The method of claim 1, further comprising preventing performing thesecond action when the rotational angle of the parent segment is betweenthe first rotational limit for the first spatial zone and the secondrotational limit for the first spatial zone.
 9. The method of claim 1,further comprising preventing performing the first action when therotational angle of the parent segment is between the first rotationallimit for the second spatial zone and the second rotational limit forthe second spatial zone.
 10. The method of claim 1, further comprisingsetting a first rotational limit and a second rotational limit for eachof an additional plurality of spatial zones.
 11. The method of claim 1,further comprising setting the first rotational limit for the secondspatial zone and the second rotational limit for the first spatial zoneat a same value of the rotational angle of the parent segment.
 12. Themethod of claim 1, further comprising setting the first rotational limitand the second rotational limit for each spatial zone to form anintervening space between the spatial zones.
 13. The method of claim 1,further comprising representing an upper arm of the motion capturesubject with the parent segment and representing a forearm, a wrist, anda finger of the motion capture subject with the child segment.
 14. Themethod of claim 1, further comprising representing a forearm of themotion capture subject with the parent segment and representing a wristand a finger of the motion capture subject with the child segment.